1.1 This specification covers manganese-vanadium-nickel alloy steel plates intended primarily for welded layered pressure vessels. 1.2 Plates under this specification are available in two grades having different strengt This specification covers manganese-vanadium-nickel alloy steel plates intended primarily for welded layered pressure vessels. Plates that shall be used are of Grades C and D and their maximum thickness is limited only by the capacity of the chemical c